Method and device for operating a fluorescent tube in an energy saving manner

ABSTRACT

The invention relates to an energy-saving operating method and an apparatus for energy-saving operation of a fluorescent tube, especially a T5 fluorescent tube. In a first operating mode, heat current is applied to an incandescent filament at one end of the fluorescent tube. Moreover, in the first operating mode, another heat current is applied to another incandescent filament at an end of the fluorescent tube opposite to said one end. The other incandescent filament is connected to energy-saving circuitry. In a second operating mode, the application of the heat current to the incandescent filament and of the other heat current and the other incandescent filament is interrupted. Monitoring means are provided, which are comprised by electronic circuitry, to monitor an operating parameter of the other incandescent filament in the first and second operating modes. The electronic circuitry controls a time period of application of the other heat current to the other incandescent filament in dependence on a time period of application of the heat current to the incandescent filament, in response to the operating parameter being monitored.

The invention relates to an energy-saving operating method and anapparatus for energy-saving operation of a fluorescent tube, especiallya T5 fluorescent tube.

It is frequent practice nowadays to operate T5 fluorescent tubes inholders made for T8 fluorescent tubes which means that existing lampholders for older T8 fluorescent tubes are being made use of for modernT5 fluorescent tubes. To be able to do that, a first adapter is disposedat a first end of the T5 fluorescent tube and a second adapter isdisposed at a second end of the T5 fluorescent tube in order tocompensate a difference in length between the shorter T5 fluorescenttubes and the longer T8 fluorescent tubes. An electronic ballast means(EVG) is arranged at the second adapter so as to have the fluorescenttube perform in energy-saving manner. To this end, the electronicballast means generates a high frequency voltage and controls switch-onand switch-off of a heat current for preheating the incandescentfilaments provided at the two ends of the T5 fluorescent tube prior tothe ignition of the T5 fluorescent tube and also in the dimming mode.For optimum operation of the T5 fluorescent tube, heat current must besupplied simultaneously to the incandescent filaments at both ends ofthe T5 fluorescent tube. Electronic circuitry provided at the secondadapter controls the supply of heat current to the incandescent filamentat the first end of the T5 fluorescent tube. At the other end, this taskis accomplished by the electronic ballast means.

It is known from the international patent application PCT/DE01/04139 totransmit a signal optically, especially in the infrared spectral range,or through an additional signal line from the electronic ballast meansto the electronic circuitry for synchronizing the switch-on andswitch-off of the heat current at the two ends of the T5 fluorescenttube. It is a disadvantage of the optical signal transmission that thelight path can be disturbed by such things as dust or particles. Use ofan additional line makes it necessary to lay such a line which involvesextra costs and thus is disadvantageous, too.

It is the object of the invention to provide an improved method and animproved apparatus for energy-saving operation of a fluorescent tube,especially a T5 fluorescent tube, permitting the heat current at theincandescent filament of the fluorescent tube to be controlledindependently of any unfavorable external influences.

This object is met, in accordance with the invention, by a methodaccording to independent claim 1 and apparatus according to independentclaims 5 and 8.

As an essential concept, the invention provides for monitoring anoperating parameter of the incandescent filament at one end of thefluorescent tube, formed opposite another end of the fluorescent tube.An electronic ballast means (EVG) is arranged at the other end of thefluorescent tube. Monitoring of the operating parameter is effected bymonitoring means belonging to electronic circuitry which controlsswitch-off/switch-on of the heat current for the incandescent filamentat the one end in response to the operating parameter being monitored.No signals are exchanged between the electronic circuitry and theenergy-saving means via an optical transmission path or a signal line,as provided in the prior art. Therefore, conditions during operation ofthe fluorescent tube that might obstruct the signal transmission betweenthe energy-saving means and the electronic circuitry are prevented fromhaving any influence on the automatic control of the application of heatcurrent to the incandescent filament at the one end. The fluorescenttubes thus can be operated reliably in energy-saving fashion even underoperating conditions which occur, for instance, when moisture or dirtcause deposits to form on the fluorescent tube or associated components,thereby obstructing the optical signal transmission. The field ofapplication of the energy-saving means is broadened accordingly.

Monitoring of the operating parameter of the incandescent filament whichis not coupled to the energy-saving means makes it possible tosynchronize the timing of switch-on/switch-off of the heat currentssupplying the incandescent filament as well as the duration of theapplication of heat current to the incandescent filament which iscoupled to the energy-saving means. Hereby, the application of therespective heat current to two incandescent filaments either can beshifted in time with respect to each other or be carried outsimultaneously. This is true both for switch-on and switch-off of theheat current.

An operating parameter especially well suited for being monitored bymonitoring means of the electronic circuitry is a maintaining voltagedependent on frequency at the other incandescent filament which is notcoupled to the electronic ballast means.

The frequency-dependent maintaining voltage may be used conveniently toinduce a voltage dependent on frequency in a resonant circuit and makeuse of said voltage as an indicator of the need to switch-on/switch-offthe heat current for the incandescent filament. When operating thefluorescent tube in a dimming mode the frequency of the maintainingvoltage changes at the incandescent filament not coupled to theelectronic ballast means. This change in frequency and the resultingdifferent voltage induced in the resonant circuit are utilized as acontrol signal for varying the application of heat current to theincandescent filament. The electronic circuitry which is formedseparately of the electronic ballast means and coupled to theincandescent filament is designed in such a way that the control of theheat current at the incandescent filament, in response to the operatingparameter monitored, is performed automatically.

The method and apparatus with which an operating parameter of theincandescent filament is taken as the starting base for control of theapplication of heat current to the incandescent filament can be utilizedconveniently to obtain energy-saving performance of a T5 fluorescenttube. When T5 fluorescent tubes are used in a lamp holder originallyprovided for a different fluorescent tube model, such as a T8 lamp, theelectronic ballast means and/or the electronic circuitry may beintegrated in adapters serving to hold the T5 lamp in the conventionalholder.

Based on an embodiment, the invention will be explained below withreference to a drawing, in which:

FIG. 1 shows an arrangement for energy-saving operation of a T5fluorescent tube in two T8 fluorescent tube holders;

FIG. 2 shows electronic circuitry for control of the heat current of anincandescent filament at the end remote from the electronic ballastmeans of a T5 fluorescent tube in the arrangement illustrated in FIG. 1;

FIG. 3 shows another arrangement for energy-saving operation of a T5fluorescent tube in two TB fluorescent tube holders; and

FIG. 4 shows electronic circuitry for control of the heat current of anincandescent filament at the end remote from the electronic ballastmeans of a T5 fluorescent tube in the other arrangement illustrated inFIG. 3.

FIG. 1 shows an arrangement for operating a modern T5 fluorescent tube 1in a first T8 fluorescent tube holder 2 and a second T8 fluorescent tubeholder 3. The first and second T8 fluorescent tube holders 2, 3 eachcomprise two receptacles 4, 5 and 6, 7, respectively. A first adapter 9is disposed between a first end 8 of the T5 fluorescent tube 1 and thefirst TB fluorescent tube holder 2. A second adapter 11 is disposedbetween a second end 10 of the T5 fluorescent tube 1 and the second T8fluorescent tube holder 3. Connecting pins 12 and 13, respectively, ofthe first adapter 9 are connected for electrical conduction to thereceptacles 4 and 5, respectively, of the first T8 fluorescent tubeholder 2. Similarly, connecting pins 14 and 15, respectively, of thesecond adapter 11 are connected for electrical conduction to thereceptacles 6 and 7, respectively, of the second T8 fluorescent tubeholder 3. An electronic ballast means 16 is arranged on the secondadapter 11. Two connecting cables 17 and 18, respectively, connect afirst connector socket 19 and a second connector socket 20 of theelectronic ballast means 16 to the connecting pins 14 and 15 of thesecond adapter 11. In this way the electronic ballast means 16 issupplied with electrical voltage. The electronic ballast means 16comprises a plurality of electronic components 21, 22, and 23; theirconcrete design may be selected by the skilled artisan for an electronicballast known per se, depending on the particular case of applicationfor energy-saving operation of the fluorescent tube. The electronicballast means 16 generates a high frequency signal which is passed onthrough a third connector socket 24 and a fourth connector socket 25 viatwo leads 26 and 27 to receiving sockets 28 and 29 of the second adapter11. A first incandescent filament 32 is connected electricallyconductively to the high frequency signal by way of contact pins 30 and31 of the second end 10 of the T5 fluorescent tube which pins arearranged in the receiving sockets 28 and 29. A second incandescentfilament 33 at the first end 8 of the T5 fluorescent tube 1 is connectedto electronic circuitry 38 through contact pins 34 and 35 andcorresponding receptacles 36 and 37 of the first adapter 9. Theelectronic circuitry 38 likewise is connected to the connecting pins 12and 13 of the first T8 fluorescent tube holder 2. It is required bothfor a hot start of the T5 fluorescent tube 1 and for smooth dimmingoperation of the T5 fluorescent tube 1 that the first incandescentfilament 32 and the second incandescent filament 33 are heated. Duringundimmed continuous operation, on the other hand, the first incandescentfilament 32 and the second incandescent filament 33 must not be heated.Synchronized heating of the first incandescent filament 32 and thesecond incandescent filament 33 is achieved, for instance, bytransmitting a signal from an infrared light emitting diode 39 to aphotosensitive diode 40, whereby the electronic circuitry 38 is causedto heat the second incandescent filament 33 or to stop heating it.

FIG. 2 illustrates an embodiment of the electronic circuitry 38. Likefeatures are marked by the same reference numerals as in FIG. 1. Asystem voltage across receptacles 4 and 5 of the T8 fluorescent tubeholder 2 is supplied to the electronic circuitry 38 at connecting pins12 and 13 (cf. FIG. 1). This normally is the mains alternating currentof 220 V.

The second incandescent filament 33 which is conductively connected toterminals 36 and 37 is supplied with heat current through two oppositelywound half-coils 41 and 42. Because of the opposed winding sense of thetwo half-coils 41 and 42, the heat current of the incandescent coil 33(not shown in FIG. 2) does not induce voltage in a second coil 43.Voltage is induced in the second coil 43 only by the high frequency lampcurrent which flows through one of the two half-coils. The highfrequency lamp current flows in and out through only one of the twoterminals 12 or 13. The voltage induced in the second coil 43 isrectified by means of a diode 44. A charging capacitor 45 is charged bythe induced direct voltage. A resistor 46 and a capacitor 47 act as afilter means.

A voltage differential occurring between points 48 and 49 of the circuitarrangement is determined by a drop in voltage across a resistor 50 anda photosensitive diode 51 (identical with the photosensitive diode 40 inFIG. 1) and depends on the incidence of light upon photodiode 51. Thedifference in voltage between points 48 and 49 is identical with thedifference in voltage between a gate and a source of a field effecttransistor 52. The field effect transistor 52 is a self-blocking endchannel field effect transistor which is mounted so as to be thermallyconductive. It will fully connect through at a voltage differential ofabout +5 V between gate and source. Once connected through, the fieldeffect transistor 52 shortcircuits the second incandescent filament 33(not shown in FIG. 2) between the terminals 36 and 37 through a bridgerecitifer 53. Zener diodes 54 and 55 and a resistor 56 serve as voltagelimiters. A resistor 57 serves to determine an operating point of thefield effect transistor 52. A light emitting diode 58 together with aseries resistor 59 supply optical information as to whether or not thecircuit is operating correctly. In case of overheating of the fieldeffect transistor 52, a fuse 60 positioned near the field effecttransistor 52 interrupts the supply of current, so that a temperaturesafety-fuse is given.

FIG. 3 shows a second arrangement for energy-saving operation of a T5fluorescent tube. In contrast to the arrangement as depicted in FIG. 1there is no optical signal transmission path between the electroniccircuitry 38 provided at the first adapter 9 and the electronic ballastmeans 16 provided at the second adapter 11. The task of the electroniccircuitry 38 in the first adapter 9, to supply heat current, whenneeded, to the second incandescent filament 33 of the T5 fluorescenttube 1 is fulfilled here by electronic circuitry of which an embodimentis illustrated in FIG. 4.

FIG. 4 is a detailed presentation of an embodiment of the electroniccircuitry 38 devised for use in the arrangement illustrated in FIG. 3.The same reference numerals in FIGS. 2 and 4 designate like features. Asmay be seen in FIG. 4, a capacitor 61 is arranged in parallel with thesecond coil 43. In this manner a parallel resonant circuit is obtainedwhich is tuned such that a maximum voltage amplitude occurs between apoint 62 and a point 63 at the high frequency of the lamp current atwhich the T5 fluorescent tube 1 generates a maximum light quantity. Inthe dimming mode, the frequency for operating the T5 fluorescent tube isincreased still further. Under such circumstances the voltage amplitudeoccurring between points 62 and 63 decreases. This voltage amplitudeinfluences the voltage differential between the gate and the source ofthe field effect transistor 52. The parallel resonant circuit formed bythe second coil 43 and the capacitor 61 thus replaces the function ofthe photosensitive photodiode 51 provided in the circuit according toFIG. 2. Furthermore, the electronic circuitry shown in FIG. 4 comprisesdiodes 64 and 65 which prevent the current from flowing back. Otherwisethe functioning of the electronic circuitry according to FIG. 4 isidentical with that of the electronic circuitry described above withreference to FIG. 2.

When the fluorescent tube is turned on there is not yet a high frequencysignal at the inputs of the T8 fluorescent tube holder. Low frequencycurrent (50 Hz mains current) flows through the half-coils 41 and 42 andalso through the second incandescent filament 33 which is connected tothe terminals 36 and 37. After firing of the T5 fluorescent tube, highfrequency current flows through both half-coils 41 and 42. Hereby,voltage is induced in the parallel resonant circuit formed by the coil43 and the capacitor 61. The charging capacitor 45 is charged, and thevoltage at the charging capacitor 45 is smoothed by means of theresistor 46 and the capacitor 47. The capacitor 47, additionally, actsas a timing delay.

The voltage induced in the parallel resonant circuit causes a positivevoltage differential between the gate and the source of the field effecttransistor 52. Thereby, the field effect transistor 52 is connectedthrough to shortcircuit the second incandescent filament 33 (not shownin FIG. 4) between the terminals 36 and 37 by way of the bridgerectifier 53. Consequently, when the field effect transistor 52 isconnected through, heat current no longer flows through the secondincandescent filament 33 which is connected to the terminals 36 and 37.

In the dimming range, the frequency is raised at which the T5fluorescent tube is operated. That causes the voltage induced in theresonant circuit to drop. A reduction of the induced voltage, at thesame time, leads to a decrease of the difference in voltage between thegate and the source of the field effect transistor 52. As the voltagedifferential between gate and source goes down, the field effecttransistor 52 begins to block. Under these circumstances the secondincandescent filament 33 (not shown in FIG. 4) is not short-circuitedany longer through the bridge rectifier 53 so that, once again, heatcurrent can flow through the second incandescent filament 33 which isconnected to the terminals 36 and 37. A resistance value within theorder of magnitude of the resistance value of the incandescent filamentmay be allocated to the branch including the field effect transistor.Part of the current thus flows through the field effect transistor andanother part through the incandescent filament. The heat current flowingthrough the second incandescent filament 33, therefore, is inverselyproportional to the current flowing through the field effect transistor52.

The features of the invention disclosed in the specification above, inthe claims and the drawing may be important for implementing theinvention in its various embodiments, both individually and in anycombination.

1. An energy-saving operating method for a fluorescent tube, the methodcomprising the following steps: applying heat current to an incandescentfilament at one end of the fluorescent tube, in a first operating mode,the incandescent filament being connected to electronic energy-savingcircuitry; applying another heat current to another incandescentfilament at an end opposite to said one end of the fluorescent tube, theother incandescent filament being connected to electronic circuitrywhich is separate from the electronic energy-saving circuitry; andinterrupting the application of the heat current and the other heatcurrent to the incandescent filament and the other incandescentfilament, respectively, in a second operating mode; wherein an operatingparameter of the other incandescent filament is monitored, in the firstand second operating modes, by monitoring means which are comprised bythe electronic circuitry so as to control a time period of applicationof the other heat current to the other incandescent filament independence on a time period of application of the heat current to theincandescent filament by means of the electronic circuitry in responseto the operating parameter being monitored.
 2. The method as claimed inclaim 1, wherein the operating parameter being monitored of the otherincandescent filament is a maintaining voltage dependent on frequency atthe other incandescent filament.
 3. The method as claimed in claim 2,wherein a voltage dependent on frequency and induced in a resonantcircuit is utilized for monitoring the frequency of the maintainingvoltage.
 4. The method as claimed in any claim 1, wherein in the firstoperating mode, the fluorescent tube is operated in a dimming mode. 5.An apparatus for energy-saving operation of a fluorescent tube,especially a T5 fluorescent tube, comprising: electronic energy-savingcircuitry adapted to be coupled to an incandescent filament at one endof the fluorescent tube to control application of heat current to theincandescent filament; and electronic circuitry, separate from theelectronic energy-saving circuitry, adapted to be coupled to anotherincandescent filament at an end opposite to said one end of thefluorescent tube to control application of another heat current to saidother incandescent filament; the electronic circuitry comprisingmonitoring means to monitor an operating parameter of said otherincandescent filament so that switch-on/switch-off of the application ofthe other heat current to the other incandescent filament can becontrolled in dependence on the switch-off/switch-on of the applicationof the heat current to the incandescent filament by means of theelectronic circuitry in response to the operating parameter beingmonitored.
 6. The apparatus as claimed in clam 5, wherein the monitoringmeans comprise means for monitoring a frequency of a maintaining voltageapplied to the other incandescent filament.
 7. The apparatus as claimedin claim 6, wherein the means for monitoring the frequency of themaintaining voltage applied to the other incandescent filament comprisea resonant circuit.
 8. An apparatus for coupling to an incandescentfilament of a fluorescent tube, comprising electronic circuitry forcontrolling the application of heat current to the incandescent filamentin dependence on the operating mode, the electronic circuitry comprisingmonitoring means to monitor a frequency of a maintaining voltage at theincandescent filament so that the application of heat current to theincandescent filament can be switched on in a first mode of operationand interrupted in a second mode of operation by means of the electroniccircuitry in response to the frequency being monitored.
 9. (Canceled)